Server

A server is a computer or program whose job is to provide resources, data and services to other devices on a network, known as clients. The term has two meanings: it can describe a physical machine designed for continuous, reliable operation, or software acting as a service provider — a web, mail or database server, for example. In both cases the essence is the same role: listening for requests and responding to them.

How a server works

A server operates on the client–server model. A client (a browser, a mobile app, another program) sends a request — for instance to display a page — and the server processes it and returns a response, such as the page's HTML. Servers run without interruption, around the clock, handling many requests in parallel, which is why server machines are built for reliability: redundant power supplies, powerful processors, plenty of RAM and fast NVMe drives.

Depending on their function, servers are grouped into web servers (powered by software such as Nginx or Apache), mail, DNS, file, database and application servers. By form, servers are divided into physical (dedicated, bare metal) and virtual, where virtualization carves many independent instances out of a single machine.

Practical application

Every page you visit, every email you send and every file you download involves a server at work. Companies rely on servers to publish websites and stores, store data, and host applications and databases. The most common models are shared hosting (many customers on one machine), a VPS (isolated, dedicated resources with full control), and a dedicated server (an entire machine at your disposal). For mission-critical services, high availability setups are built in which the failure of a single server does not interrupt the service. The choice depends on the scale of traffic, performance requirements and the level of control needed over the environment.